The present invention relates to xe2x80x9cA process for the preparation of substituted trans-cinnamaldehyde, a natural yellow dye, from phenylpropane derivativesxe2x80x9d in which trans-cinnamaldehyde (e.g. 2,4,5-trimethoxycinnamaldehyde where R1 is xe2x80x94CHxe2x95x90CHxe2x80x94CHO, R2xe2x95x90R4xe2x95x90R5 is xe2x80x94OMe and R3xe2x95x90R6 is H; p-methoxycinnamaldehyde where R1 is xe2x80x94CHxe2x95x90CHxe2x80x94CHO, R2xe2x95x90R3xe2x95x90R5xe2x95x90R6 is H, R4 is xe2x80x94OMe and 3,4-dimethoxycinnamaldehyde where R1 is xe2x80x94CHxe2x95x90CHxe2x80x94CHO, R2xe2x95x90R5xe2x95x90R6 is H and R3xe2x95x90R4 is xe2x80x94OMe etc) of the formula I as shown below: 
These compounds can be obtained by oxidation of (R2xe2x80x94R3xe2x80x94R4xe2x80x94R5xe2x80x94R6)phenylpropane derivatives (wherein R2 to R6 equal or different, being hydrogen or hydroxy or alkyl or methylenedioxy or alkoxy groups, etc) which is, in fact, a reduced product of readily available natural phenylpropene (methyl chavicol, anethole, eugenol, methyl isoeugenol, safrole, toxic xcex2-asarone etc) bearing essential oil or the like.
Cinnamaldehyde and its substituted derivatives (e.g. p-methoxy cinnamaldehyde, 3,4-methylenedioxycinnamic aldehyde, coniferyl aldehyde etc) possess an aromatic ring bearing one or more hydroxy or dioxymethylene or alkoxy groups or the like, attached to the xcex1,xcex2-unsaturated aldehyde (i.e. CHxe2x95x90CHxe2x80x94CHO) which contribute significantly to the taste and flavour of many foods and drinks (Harbome, J. B. and Baxter, H., In: Phytochemical Dictionary, A Handbook of Bioactive Compounds from Plants, Taylor and Francis Ltd., London WC1N 2ET, 472-488 (1993)). In addition, cinnamaldehyde derivatives serve as a raw material for the preparation of a number of other perfumery aromatics. Morever, the selective reduction of the aldehyde group gives cinnamyl alcohol which possesses a pleasant and long-lasting spicy odor and complete reduction of the side chain gives phenyl propyl alcohol and its oxidation give hydrocinnamic acid (Muller, A. J., Bowers Jr, J. S., Eubanks, J. R., Geiger, C. C. and Santobianco, J. G., U.S. Pat. No. 5,939,581)) which, along with its ester, finds usage in perfumery composition. Cinnamaldehyde and its derivatives are not only found to be highly effective to prevent skin from darkening caused by irradiation of ultraviolet rays from the sun (Tomoshi, K. and Makoto, F., JP Pat. No. 58055414A2)) but also proved to be excellent in preventing falling-off of hair and also provide hair growth (Watanabe, T., Komeno, T. and Hatanaka, M., JP Pat. No. 6312916A2)). In addition, cinnamaldehyde in combination with the manure controls injurious microorganisms present in soil without any adverse effect on manure-decomposing microorganisms (Saotome, K., JP Pat. No. 58201703A2)). Further, cinnamaldehyde derivatives are useful as an intermediate for synthesis of various drugs such as anti-viral pharmaceuticals, particularly HIV protease inhibitors (Castelijns, A. M. C. F., Hogeweg, J. M. and van Nispen, S. P. J. M., U.S. Pat. No. 5,811,588) and also used in cosmetics, dyes, agrochemicals, alkaloids (Parmar, V. S., Jain, S. C., Bisht, K. S., Jain, R., Taneja, P., Jha, A., Tyagi, O. D., Prasad, A. K., Wengel, J., Olsen, C. E. and Boll, P. M., Phytochemistry, 46(4): 597-673 (1997)), perfumes, etc.
Cinnamaldehyde is identified for the first time in the year 1833 during steam distillation of Ceylon bark of cinnamon (Cinnamomum zeylanicum, family: Lauraceae) which is still one of the main source of cinnamaldehyde. It also occurs in dozens of flowers and essential oils such as Hyacinthus spp., Narcissus spp., Lavandula spp., Pogostemon cabline and Commiphora spp. and others. However, substituted cinnamaldehyde (coniferyl aldehyde or coniferaldehyde or ferula aldehyde or ferulaldehyde) occurs in a number of other plants such as Quercus spp., Acer saccharinum which, imparts a phenolic-spicy, sweet balsamic odour and is used extensively in flavour compositions. Similarly, sinapaldehyde (3,5-dimethoxy-4-hydroxycinnamaldehyde) occurs in Juglans nigra, Senra incana and p-methoxycinnamaldehyde in Acorus gramineu etc. Mostly, substituted cinnamaldehydes are yellow in color; therefore, the applicability of cinnamaldehyde can be further increased with the possibities of their uses in the area of natural dyes. However, the limited percentage of substituted cinnamaldehydes present in the plant kingdom is not sufficient to fulfill the world demand. As a result, the major amounts of cinnamaldehydes are made synthetically.
A number of proceses have been proposed to produce cinnamaldehyde and its derivatives (such as p-methoxycinnamaldehyde, dimethoxycinnamaldehyde, sinapaldehyde, trimethoxycinnamaldehyde and methylenedioxy cinnamaldehyde etc). For the most part, these methods involve reaction of the substituted benzaldehyde (such as p-methoxybenzaldehyde etc) with acetaldehyde in the presence of acid or better with alkali. Cinnamaldehyde can also be prepared by hydrolysis of cinnamylidene chloride. Good yields have been obtained by the Rosenmund reduction of cinnamic acid chloride with palladinium catalyst (March, J., In: Advanced Organic Chemistry, Reactions, Mechanisms and Structure, Wiley Eastern Ltd., New Delhi, 396-397, (1987)). Catalytic dehydrogenation of cinnamic alcohol at high temperature under reduced pressure has given good yields of cinnamaldehyde. Dry distillation of the calcium salts of cinnamic and formic acid also yields aldehyde. Isomerization of phenylethynyl carbinol in the presence of acid produces good yields of aldehyde. A practical method of producing a range of xcex1,xcex2-unsaturated aldehyde is to treat an olefin with carbon monoxide under pressure and in the presence of a catalyst (Brown, H. C. and Tsukamoto, A., J. Am. Chem. Soc., 86: 1089 (1964)) and Bedoukian, P. Z., In: Perfumery and Flavoring Synthetics, Allured Publishing Corporation, Wheaton, Ill., USA, 98-105 (1986)). Though such methods have been proven to be useful, they suffer from one or more process deficiencies. For example, in some instances processes of this type necessarily involve resort to sub-ambient temperatures, which of course, involves some considerable process control and in some cases, the reaction is effected only at a relatively high pressures and lead to reaction mixtures.
Typical prior art references include U.S. Pat Nos. 2,529,186; 2,794,813; 3,028,419 and German Patent Nos. 97,620; 1,114,798 and Soviet Union Pat. No. 1451139A1 and Czechoslovakia Pat. No. 8405411A1.
It, therefore, becomes an object of invention to provide a process for producing cinnamaldehydes such as p-methoxycinnamaldehyde, 3,4-dimethoxycinnamaldehyde, 3,4-methylenedioxycinnamaldehyde, 3,4-methylenedioxy-5-methoxycinnamaldehyde, 1-ethoxy-2-acetoxycinnamaldehyde, 1-ethoxy-2-hydroxycinnamaldehyde, sinapaldehyde, 2,5-dimethoxy-3,4-methylenedioxycinnamaldehyde, 2-methoxy-4,5-methylenedioxy cinnamaldehyde, coniferyl aldehyde, 3,4,5-trimethoxycinnamaldehyde, 2,3-dimethoxy-4,5-methylenedioxycinnamaldehyde and 2,4,5-trimethoxycinnamaldehyde or the like, by means which eliminate the above discussed disadvantages and others.
Other objectives will appear hereinafter.
The main object of the present invention is to develop a simple industrial process for the preparation of substituted cinnamaldehyde (such as p-methoxycinnamaldehyde, 3,4-dimethoxycinnamaldehyde, 2,4,5-trimethoxycinnamaldehyde etc) in one step with high yield from phenylpropane derivatives (such as dihydro methylchavicol, dihydro methyleugenol, 2,4,5-trimethoxyphenylpropane etc) which is, in fact, the hydrogenated product of readily available natural phenylpropenes (such as, methyl chavicol or anethole, methyl eugenol, highly toxic xcex2-asarone etc.)
In another object of the invention is to develop a simple process for the preparation of substituted cinnamaldehyde in high purity without any contamination of corresponding cinnamicacid and alcohol.
Yet another object of the present invention is to develop a process for the preparation of trans-cinnamaldehyde exclusively in a single step from phenylpropane derivatives.
Yet another object of the invention is to develop a simple process for the preparation of substituted cinnamaldehyde, a natural yellow dye, on commercial scale for multifarious applications such as for colouring and flavouring foods and also for pharmaceutical industries etc.
Yet another object of the invention is to develop a simple and quick process for the preparation of substituted cinnamaldehyde in a short time ranging from a few seconds to a few minutes under microwave irradiation.
Yet another object of the invention is to develop a process for the preparation of substituted cinnamaldehyde utilizing simple and cheaper dihydroproduct obtained from readily available natural phenylpropene bearing oil such as methyl chavicol, anethole, eugenol etc.
Yet another object of the present invention is to prepare substituted cinnamaldehyde utilizing otherwise toxic essential oil e.g. safrole or xcex2-asarone or the other like toxic oil thereby, enhancing the profitable use thereof.
Yet another object of the present invention is to provide a process for the preparation of 2,4,5-trimethoxycinnamaldehyde or the like for the first time which is useful as a simple starting material for synthesis of corresponding cinnamic acid, esters, amide derivatives and other uses thereof for synthesis of heterocyclic and biologically active compounds.
Accordingly, the present invention provides a process for the preparation of substituted trans-cinnamaldehyde from phenylpropane derivatives utilizing 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as an efficient oxidizing agent in the presence of catalyst namely acetic acid, p-toluenesulphonic acid, silica gel.
Accordingly the present invention provides, a process for the preparation of substituted trans cinnamaldehyde, a natural yellow dye, of Formula 1 ##STR## as shown in FIG. 4 of the accompanying drawing wherein, R1 is fixed as a xe2x80x94CHxe2x95x90CHxe2x80x94CHO, however, R2, R3, R4, R5, R6 are independently selected from i) a hydrogen atoms ii) a alkoxy group but atleast two of them from R2, R3, R4, R5, R6 are hydrogen atom or a alkoxy group but one methylenedioxy group with combination of either hydroxyl group, alkoxy group, alkyl group having 1-2 carbon atoms, aryl group or hydrogen atom or a alkoxy group but one hydroxyl group with combination of either methylenedioxy group, hydroxyl group, alkoxy group, alkyl group having 1-2 carbon atoms, aryl group or hydrogen atom; iii) a methylenedioxy with atleast three of them R2, R3, R4, R5, R6 are combination of either alkoxy, hydroxy group, alkyl group having 1-2 carbon atoms, aryl group or hydrogen atom; vi) a hydroxyl group but atleast one of them from R2, R3, R4, R5, R6 is hydrogen atom with combination of either alkoxy, hydroxyl group, methylenedioxy group, alkyl group having 1-2 carbon atoms, aryl group or hydrogen atom; vii) a protected hydroxyl group such as acetyl, benzyl, but atleast one of them from R2, R3, R4, R5, R6 is hydrogen atom with combination of either alkoxy, hydroxyl group, methylenedioxy group, alkyl group having 1-2 carbon atoms, aryl group or hydrogen atom, obtained from corresponding (R2xe2x80x94R3xe2x80x94R4xe2x80x94R5xe2x80x94R6)phenylpropane derivatives, said process comprising oxidizing substituted phenylpropane derivatives in presence of a solvent and a catalyst using an oxidizing agent in a mole ratio of 1:1 to 1:8 to the phenyl propane derivatives at a temperature between xe2x88x9215 to +210xc2x0 C. for a period of 30 minutes to 48 hours, removing the solvent under reduced pressure and isolating the product in a conventional manner to obtain a yield between 68-82% of trans cinnamaldehyde of formula 1.
It is worthwhile to mention that the above cost effective process is an accidental result of two individual steps (i.e. dehydrogenation and oxidation) observed for the first time during DDQ assisted oxidation of phenylpropane which is, in fact, the reduced product of readily available natural phenylpropenes (such as methyl chavicol, eugenol, dimethylisoeugenol etc.) including some toxic and an internationally banned isomer of phenylpropene derivatives such as safrole and -asarone.
In one embodiment of the invention, the solvent used is selected from the group consisting of diethyl ether, tetrahydrofuran, dimethoxyethane, dioxane, diphenylether, chlorinated solvent selected from such as dichloromethane, chloroform and o-dichlobenzene, an aromatic hydrocarbon selected from benzene, toluene, xylene and organic acid selected from formic acid, acetic acid.
In another embodiment of the invention, the oxidizing agent used is selected from the group consisting of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), p-chloranil, pyridinium chlorochromate (PCC), tBuOOH, CrO3 and a mixtures thereof.
In still another embodiment of the invention, the mole ratio of oxidizing agent to reactant is ranging from 1:1.5 to 1:5.
In yet another embodiment of the present invention, the reaction temperature is ranging from 30xc2x0 C. to 140xc2x0 C.
In yet another embodiment of the present invention, reaction period is ranging 4-16 hours.
In yet another embodiment of the present invention, the catalyst used is selected from a group comprising hydrochloric acid, sulfuric acid, Cu(I) or Fe(III) salt, periodic acid, organic acid selected from acetic acid, propionic acid, butyric acid, ion exchange resin selected from IR-120H and a sulphonated polystyrene resin, para-toluenesulphonic acid (PTSA) and amberlyst such as amberlyst 15.
In yet another embodiment of the present invention, the starting material phenylpropane used is obtained by reduction of allylbenzene or phenyl propene derivatives or widely available natural allyl/phenyl propene derivatives exiting in all three isomeric forms.
In yet another embodiment of the present invention, the oxidation of phenylpropane provides trans-cinnamaldehyde, which is similar to the isomer produced by plants.
In yet another embodiment of the present invention, toxic beta (cis) and xcex3-isomer are converted into value added natural dyes.
In yet another embodiment of the present invention, an internationally banned beta-asarone from Acorus calamus is utilized by its conversion into a useful natural yellow dye.
In yet another embodiment of the present invention, the process is capable of preparing cinnamaldehyde derivatives on commercial scale.
In yet another embodiment of the present invention, the above process is capable of providing some new kind of cinnamaldehyde derivatives, which are useful as natural colorants, antioxidant and antimicrobial agents.
In yet another embodiment of the present invention, the above process provides DDQH2 (by product) 91-94% and its regeneration into DDQ also reduces the cost of production of cinnamaldehyde derivatives.
In yet another embodiment of the present invention, the above process is capable to oxidize phenyl alkane having 2nxe2x88x921 carbon atoms wherein, n varies from 2 to 6 or more into corresponding unsaturated aldehydes.
In yet another embodiment of the present invention, the above phenylpropane derivatives are capable of undergoing various kind of reactions such as halogenation, dehydrogenation, allylic halogenation, formulation, mono and/or dicarbonylation, condensation.
In yet another embodiment of the present invention, the above process provides cinnamaldehyde derivatives without any contamination of corresponding acid and alcohol.
In yet another embodiment of the present invention, in above process some of cinnamaldehyde such as 2,4,5-trimethoxycinnamaldehyde is obtained in good yield, which finds application as a simple starting material for the synthesis of corresponding various new unsaturated acids, esters, amides, alcohol derivatives.
In yet another embodiment of the present invention, some of cinnamaldehyde such as 2,4,5-trimethoxycinnamaldehyde is obtained in good yield which finds application as a simple starting material for the synthesis of corresponding various new dihydro (saturated) acids, esters, amides and alcohols derivatives.
In yet another embodiment of the present invention, the products obtained are (i) 2,4,5-trimethoxycinnamaldehyde where R1 is xe2x80x94CHxe2x95x90CHxe2x80x94CHO, R2xe2x95x90R4xe2x95x90R5 is xe2x80x94OMe and R3xe2x95x90R6 is H, (ii) p-methoxycinnamaldehyde where R1 is xe2x80x94CHxe2x95x90CHxe2x80x94CHO, R2xe2x95x90R3xe2x95x90R5xe2x95x90R6 is H and R4 is xe2x80x94OMe and (iii) 3,4-dimethoxycinnamaldehyde where R1 is xe2x80x94CHxe2x95x90CHxe2x80x94CHO, R2xe2x95x90R5xe2x95x90R6xe2x95x90H and R3xe2x95x90R4 is xe2x80x94OMe.
In one more embodiment the present invention provides a process for the preparation of substituted trans-cinnamaldehyde, a natural yellow dye, of Formula 1, said process comprising oxidizing substituted phenylpropane derivatives in presence of a solvent and a catalyst using an oxidizing agent in a mole ratio of 1 to 20 with a solid support under micro wave radiation at a medium power 600 W for a period ranging from 20 seconds to 12 minutes, removing the solvent under reduced pressure and isolating the product in a conventional manner to obtain the trans-cinnamaldehyde of formula 1.
In yet another embodiment of the present invention, the solid support used is selected from a group comprising celite, silica gel, molecular sieve and alumina.
In yet another embodiment of the present invention, the products obtained through the microwave radiation process are (i) 2,4,5-trimethoxycinnamaldehyde where R1 is xe2x80x94CHxe2x95x90CHxe2x80x94CHO, R2xe2x95x90R4xe2x95x90R5 is xe2x80x94OMe and R3xe2x95x90R6 is H, (ii) p-methoxycinnamaldehyde where R1 is xe2x80x94CHxe2x95x90CHxe2x80x94CHO, R2xe2x95x90R3xe2x95x90R5xe2x95x90R6 is H and R4 is xe2x80x94OMe and (iii) 3,4-dimethoxycinnamaldehyde where R1 is xe2x80x94CHxe2x95x90CHxe2x80x94CHO, R2xe2x95x90R5xe2x95x90R6 is H and R3xe2x95x90R4 is xe2x80x94OMe.
In short, the present invention provides a process for the preparation of substituted trans-cinnamaldehyde, a natural yellow dye, from phenylpropane derivatives wherein R.sup.1 is fixed as a xe2x80x94CHxe2x95x90CHxe2x80x94CHO, however, R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6 are independently; i) a hydrogen atoms ii) a alkoxy group but atleast two of them from R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6 are hydrogen atom or a alkoxy group but one methylenedioxy group with combination of either hydroxyl group, alkoxy group, alkyl group having 1-2 carbon atoms, aryl group or hydrogen atom or a alkoxy group but one hydroxyl group with combination of either methylenedioxy group, hydroxyl group, alkoxy group, alkyl group having 1-2 carbon atoms, aryl group or hydrogen atom; iii) a methylenedioxy with atleast three of them from R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6 are combination of either alkoxy, hydroxy group, alkyl group having 1-2 carbon atoms, aryl group and hydrogen atom; iv) a hydroxyl group but atleast one of them from R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6 is hydrogen atom with combination of either alkoxy, hydroxyl group, methylenedioxy group, alkyl group having 1-2 carbon atoms, aryl group or hydrogen atom; v) a protected hydroxyl group such as acetyl, benzyl, etc but atleast one of them from R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6 is hydrogen atom with combination of either alkoxy, hydroxyl group, methylenedioxy group, alkyl group having 1-2 carbon atoms, aryl group and hydrogen atom or the like, obtained from corresponding (R2xe2x80x94R3xe2x80x94R4xe2x80x94R5xe2x80x94R6)phenylpropane derivatives (e.g. dihydro anethole where R2xe2x95x90R3xe2x95x90R5xe2x95x90R6 is H; R4 is xe2x80x94OMe; dihydro methyl eugenol where R2xe2x95x90R5xe2x95x90R6 is H; R3xe2x95x90R4 is xe2x80x94OMe and dihydro asarone where R2xe2x95x90R4xe2x95x90R5 is xe2x80x94OMe; R3xe2x95x90R6 is H etc) and the above process comprising the steps of (a) providing phenylpropane such as but not limited to 2,4,5-trimethoxyphenylpropane (dihydroasarone) in the following solvents namely ether such as but not limited to diethyl ether, tetrahydrofuran, dimethoxyethane, dioxane, diphenylether and the like; chlorinated solvents such as but not limited to dichloromethane, chloroform, o-dichlobenzene; an aromatic hydrocarbon such as but not limited to benzene, toluene, xylene; organic acid such as but not limited to formic acid, acetic acid and the like; (b) oxidation of phenylpropane derivatives in the presence of oxidizing reagents such as but not the limited to 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) or p-chloranil or pyridinium chlorochromate (PCC) or tBuOOH or CrO3 or a combination of reagents and the like and the amount thereof to be used is in the ration of 1-20 times moles, preferably 1.5-8 times moles, reaction temperature varies from xe2x88x9215xc2x0 C. to +210xc2x0 C., preferably 30xc2x0 C. to 140xc2x0 C., reaction period varies from 30 minutes to 48 hours, preferably 4-16 hours; (c) oxidation step proceeds more smoothly along with higher yield in presence of catalysts mainly mineral acid such as but not limited to hydrochloric acid, sulphuric acid or Cu(I) or Fe(III) salt or periodic acid or organic acid such as but not limited to acetic acid, propionic acid, butyric acid, ion exchange resin such as IR-120H, a sulphonated polystyrene resin, para-toluenesulphonic acid (PTSA) or amberlyst such as amberlyst 15 or absorbed above solution of phenylpropane and oxidising reagent on the following solid support such as but not limited to celite, silica gel, molecular sieve, alumina and the like in a short period ranging from 20 seconds to 12 minutes under microwave irradiation; (d) filtering the mixture and removing the solvent under reduced pressure, where the product is to be isolated in a conventional manner, i.e. extraction, distillation, recrystallization and chromatography and the yield of the product (e.g. 2,4,5-trimethoxycinnamaldehyde where R1 is xe2x80x94CHxe2x95x90CHxe2x80x94CHO, R2xe2x95x90R4xe2x95x90R5 is xe2x80x94OMe; R3xe2x95x90R6 is H; and 3,4-dimethoxycinnamaldehyde where R1 is xe2x80x94CHxe2x95x90CHxe2x80x94CHO, R2xe2x95x90R5xe2x95x90R6xe2x95x90H; R3xe2x95x90R4 is xe2x80x94OMe etc. in the above formula I) varies from 68-82%, preferably more in case of benzoquinone as a oxidising reagent.
In an embodiment of the present invention, a simple process is described in order to obtain substituted trans-cinnamaldehyde. In fact, a simple and cheaper starting material phenylpropane derivatives obtained from hydrogenation of widely available natural phenylpropene is utilized for high valued cinnamaldehyde derivatives.
In another embodiment of the present invention, a simple and one step process is described for substituted cinnmaldehydes in high puLrity and yield without contamination of corresponding acid and alcohol.
In another embodiment of the present invention, substituted cinnamaldehydes are used as a natural yellow dye for colouring food, textile and pharmaceutical products etc.
In another embodiment of the present invention is a simple process, available for commercial scale production.
Phenylpropanoids (C6-C3) comprises of the compounds in which derivatives of phenylpropene, phenylpropanone, cinnamaldehyde, cinnamal alcohol, cinnamic acid and ester are found to be biologically active and have commercial importance. Among these phenylpropanoids, the (R2xe2x80x94R3xe2x80x94R4xe2x80x94R5xe2x80x94R6) cinnamaldehyde derivatives wherein R2 to R6 equal or different, being hydrogen or hydroxy or methylenedioxy or alkoxy groups, etc are frequently present in the essential oil. As per applications concern, these cinnamaldehydes are widely used in fragrance, flavour, cosmetic, liquor and in pharmaceuticals, etc and are also utilized as pheromones, antibacterial, antifungal etc in the insect world. The wide use of cinnamaldehydes (F.E.M.A. no. 2286) ranging from flavouring agents to pharmaceuticals and their importance as an intermediate in the synthesis of biologically active compounds have always attracted attention of chemists (Muller, A. J., Bowers Jr, J. S., Eubanks, J. R., Geiger, C. C. and Santobianco, J. G., U.S. Pat. No. 5,939,581 and Castelijns, A. M. C. F., Hogeweg, J. M. and van Nispen, S. P. J. M., U.S. Pat. No. 5,811,588)). The principal source of cinnamaldehyde (synonyms: cinnamic aldehyde or 3-phenylpropenal or cinnamal or gamma-phenylacrolein or cassia aldehyde) is the bark of cinnamon (Cinnamomum zeylanicum; Lauraceae) and its fresh bark contains high levels of cinnamyl acetate which releases cinnamaldehyde by fermentation processes applied during commercial preparation by enzymatic hydrolysis and participation of the reversible aldehyde-alcohol oxidoreductase. Cinnamon leaf, on the other hand, contains large amounts of eugenol and much smaller amounts of cinnamaldehyde. Similarly, another source of cinnamaldehyde is Cinnamornum cassia which is widely used in traditional Chinese medicine (Tang, W. and Eisenbrand, G. In: Chinese Drugs of Plant Origin, Springer-Verlag, New York, pp. 319-330 (1992)) as an analgesic, stomachic and anti-inflammatory agent and its activity is found due to high percentage of cinnamaldehyde (85%). In addition, cinnamaldehyde has shown anti-mutagenic activity towards chemical mutagens or UV irradiation (Kakimuma, K., Koike, J., Kotanik, K., Ikekawa, W., Kado, T. and Nomoto, M., Agric. Biol. Chem. 48: 1905-1906 (1984); Ohta, T., Watanabe, K., Moriya, M., Shirasu, Y., Kada, T., Mutat. Res., 107: 219-227 (1983)). Cinnamaldehyde at a concentration of 4.8 xcexcg/ml inhibited the growth of L 1210 leukemia cells in culture by 50% and its aldehydydic group is found to be responsible for the above inhibition. Cinnmaldehyde also inhibited the growth of SV40-induced tumor W2K-11 in mice (CA 94: 168054k and Moon, K. H., Pack, M. Y., Drug Chem., Toxicol, 6: 521-535 (1983)).
Similarly, a number of substituted cinnamaldehydes such as ortho-methoxy cinnamaldehyde (synonym: ortho-cumeric aldehyde methyl ether), para-methoxy cinnamaldehyde (synonym: para-cumeric aldehyde methyl ether), 3,4-dimethoxy cinnamic aldehyde (synonyms: homoconiferaldehyde or methyl ferulaldehyde), para-coniferaldehyde (synonyms: ferulaldehyde or maple aldehyde or 4-hydroxy-3-methoxy cinnamic aldehyde), 3,4-methylenedioxycinnamic aldehyde (synonyms: piperonyl acrolein or heliotropylidene acetaldehyde or piperonylidene acetaldehyde), sinapaldehyde (synonym: 2,4-dimethoxy-4-hydroxy cinnamic aldehyde) are also widely used in flavour compositions, however, the odour of these substituted cinnamaldehydes bears a little organoleptic resemblance to that of cinnamaldehyde. In addition, some substituted cinnamaldehydes are known for their biological activities. 2xe2x80x2-hydroxycinnamaldehyde inhibits farnesyl-protein transferase (FPTase) (Knon, B. M.; Cho, Y. K., Lee, S. H., Nam, J. Y., Bok, S. H., Chun, S. K., Kim, J. A. and Lee, I. R., Planta Medica, 62: 183-184 (1996)) and also acts as active anticancer compound (Lee, C. W., Hong, D. H., Han, S. B., Park, S. H., Kim, H. K., Kwon, B. M. and Kim, H. M., Planta Medica, 65: 263-266 (1999)). 3xe2x80x2,4xe2x80x2-dimethoxycinnamaldehyde reduces the contractile response of guinea pig ileal strips to LTD4. Similarly, substituted cinnamaldehyde such as 4-hydroxy-3-methoxycinnamaldehyde is a potent antioxidant compound (Kikuzaki, H., Hara, S., Kawai, Y. and Nakatani, N., Phytochemistry, 52, 1307-1312 (1999)) and also found as an inducible nitric oxide synthesis (iNOS) inhibitory compound (Kim, N. Y., Pae, H. O., Ko, Y. S., Yoo, J. C., Choi, B. M., Jun; C. D., Chung, H. T., Inagaki, M., Higuchi, R. and Kim, Y. C., Planta, Medica, 65, 656-658 (1999)). However, substituted cinnamic aldehyde are found in traces in plants kingdom and alternatively, they can be obtained by chemical synthesis. Some of the important methods are:
(a) reaction of substituted benzene derivative with nitroso dimethylaniline in the presence of mineral acid and catalyst (CA 51, 7326 (1957);
(b) condensation of vinyl ether with arylaldehyde acetal (Friedrich and Hartmann, Chem. Ber., 94, 838 (1961);
(c) reaction of Grignard of bromobenzene with 1-(N-Methylanilino)propen-3-al (Jutz, Ger. Pat. 1,114,798, Oct. 12, (1961);
(d) reaction of appropriate olefin with carbon monoxide under pressure and in the presence of catalysts (U.S. Pat. No. 3,028,419, Apr. 3, (1962));
(e) claisen-Schmidt reaction of arylaldehyde with acetaldehyde offers cinnamaldehyde in the range of 12 to 30% depending upon the arylaldehyde used. The low yield of this reaction product is, perhaps, due to self-condensation of acetaldehyde (Richmond, U.S. Pat. No. 2,529,186, Nov. 7, (1950);
(f) reaction of arylaldehyde with triethyl phosphonoacetate followed by reduction of ethyl cinnamate with lithium aluminium hydride (LAH) to corresponding cinnamyl alcohol and then oxidation of cinnamyl alcohol with MnO2 into cinnamaldehyde (Rajasekhar, D. and Subbaraju, G. V. Indian. J. Chem. 38, 837-838 (1999)). However, this is a multistep process and requires expensive reagents;
(g) reaction of cinnamic acid with thionyl chloride followed by reduction with bis(triphenylphosphine)tetrahydroborate copper (El-Feraly, F. S. and Hoffstetter, M. D. J. Nat. Prod. 43, 407 (1980);
(h) reaction of arylaldehyde with poisonous potassium cyanide reagent (Deuchert, S. K., Hertenstein, U. and Hunig, S., Synthesis, 777 (1973); and
(i) reaction of N,N-dimethylbenzamide with lithium diethoxyaluminium hydride (Perun, T. J., Zeftel, L., Nelb, R. G. and Tarbell, D. S., J. Org. Chem., 28, 2937 (1963).
All the above methods have various limitations, for example, low yield, expensive reagents and formation of unwanted side products. It is rather curious that in spite of very large quantities of cinnamaldehyde manufactured annually, the chemical and patent literatures on the subject of its manufacture are quite meager. Keeping in view of all the above problem, we have invented a simple industrial process for preparation of substituted cinnamaldehyde in a single step from phenylpropane. To the best of the applicants knowledge, oxidation of phenylpropane derivatives into substituted cinnamaldehyde derivatives have not been reported earlier. This simple starting material can be obtained by reduction of double bond of phenylpropenes bearing essential oil (such as methyl chavicol, anethole, methyl eugenol, safrole, xcex2-asarone etc). In addition, phenylpropane derivatives can be prepared by Grignard reaction of benzyl chloride derivatives with diethyl sulphate (Organic Synthesis, Coll. Vol 1, pp 471). However, it is worthwhile to mention that the applicants"" above process for the preparation of substituted cinnamaldehyde has been invented during the development of a process for the preparation of pharmacological active trans-phenylpropene (xcex1-asarone) (Janusz, P., Bozena, L., Alina, T. D., Barbara, L., Stanislaw, W., Danuta, S., Jacek, P., Roman, K., Jacek, C., Malgorzata, S., Zdzislaw, C., J. Med. Chem., 43, 3671-3676 (2000)) from 2,4,5-trimethoxyphenylpropane, a reduced product of toxic xcex2-asarone.
Phenylpropenes, widely used in fragrance, flavour, cosmetic, liquor, whisky, and pharmaceutical industries, exist in three isomeric form (i.e. xcex1, xcex2 and xcex3), however, cis-isomeric form of phenylpropene (such as xcex2-asarone) has been recently proved to be carcinogenic and toxic (Taylor, J. M., Jones, W. I., Hogan, E. C., Gross, M. A., David, D. A. and Cook, E. L., Toxicol. Appl. Pharmacol., 10: 405 (1967); Keller, K.; Odenthal, K. P. and Leng, P. E., Planta Medica, 1: 6-9 (1985) and Kim, S. C., Liem, A., Stewart, B. C. and Miller, J. A., Carcinogensis, 20(7), 1303-1307 (1999)) and therefore, banned for any kind of use in flavour, perfumery and pharmaceutical industries. Cis-anethol is found to be 15 times more toxic than trans-anethol. Similarly, xcex3-isomeric form of phenylpropene (such as safrole) is also found carcinogenic (Daimon, H., Sawada, S., Asakura, S. and Sagami, F., Carcinogenesis, 19(1): 141-146, (1998) and Liu, T. Y., Chen, C. C., Chen, C. L. and Chi, C. W., Food and Chemical Toxicology, 37(7): 697-702, (1999). In view of above problem, most affected plant is Acorus calamus (family:Araceae) in which percentage of toxic xcex2-asarone depends upon the varieties of A. calamus (Riaz, M., Shadab, Q., Chaudhary, F. M., Hamdard Medicus 38(2): 50-62 (1995) and McGuffin, M., Hobbs, C., Upton, R. and Goldberg, A., In: American Herbal Products Association""s Botanical Safety Handbook, CRC Press, Inc.; Boca Raton, Fla.; USA, 231, (1997)). The content of xcex2-asarone in the triploid variety is 8-19%, while xcex2-asarone reaches upto 96% in the tetraploid and hexaploid varieties (extensively found in Asian countries). In contrast, ,B-asarone is not found in the diploid variety. As a result, the calamus oil obtained from North American diploid strain (zero, xcex2-asarone) and East European triploid strain (upto 12% xcex2-asarone) are allowed for clinical effectiveness and safety while the calamus oil produced in Asian belt (such as India, Pakistan, Bangladesh, Nepal, Japan and China) has diminished the market potential of calamus oil due to high percentage of xcex2-asarone ranging from 70 to 96% (Mazza, G., J. of Chromatography 328:179-206 (1985); Nigam, M. C., Ateeque, A., Misra, L. N. and Ahmad, A., Indian Perfumer 34: 282-285 (1990) and Bonaccorsi, I., Cortroneo, A., Chowdhury, J. U. and Yusuf, M., Essenze Derv. Agrum, 67(4): 392-402 (1997)). Therefore, the applicants"" objective is to utilize toxic xcex2-asarone (cis-2,4,5-trimethoxyphenyl-1-propene) as a simple starting material for value added products via its reduced product (2,4,5-trimethoxyphenylpropane) which has recently been found useful as a new aroma molecule with atleast six to four times less toxic than xcex2-asarone or calamus oil (Sinha, A. K., U.S. Ser. No. 09/652,376 filed Aug. 31, (2000)). Further, 2,4,5-trimethoxyphenylpropane appeared to us as a simple intermediate for the preparation of trans-2,4,5-trimethoxyphenyl-1-propene (xcex1-asarone).
Interestingly, 2,4,5-trimethoxyphenylpropane when treated with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) furnished xcex1-asarone (compared with standard xcex1-asarone) and an intense yellow coloured spot with some unreacted starting material (clearly visible on TLC plate). Increase in the amount of DDQ further favoured the formation of yellow colouring material rather than the xcex1-asarone. All three products were separated on column chromatography in which yellow solid (mp 140xc2x0 C.) showed IR absorption band at 1648 cmxe2x88x921 (conjugated Cxe2x95x90O) and also gave positive 2,4-DNP test, thus, confirming the presence of carbonyl group. UV spectra of yellow solid (xcexmax 244, 298, 366 nm) confirmed an increase in conjugation than the starting material 2,4,5-trimethoxyphenylpropane (288 nm) and xcex2-asarone (269, 301 nm). 1H NMR (FIG. 1) of yellow solid showed the 14 number of protons (see Example I) in which two doublets and one doublet of doublet for three protons appeared at xcex4 9.65 (1H, d, J=7.8 Hz), 7.81 (1H, d, J=15.8 Hz) and xcex4 6.64 (1H, dd, J=15.8 Hz, J=7.8 Hz) respectively. Further, the position of two aromatic singlet protons and three singlet for nine protons for three trimethoxy groups were more or less at same xcex4 value as compared to xcex2-asarone (Patra, A. and Mitra, A. K., Phytochemistry, 44: 668-669 (1981)). IR and 1H NMR has supported the possibility of unsaturated aldehyde group (xe2x80x94CHxe2x95x90CHxe2x80x94CHO) attached with trimethoxy (nine protons) substituted phenyl ring (two protons). Similarly, the 13C NMR (FIG. 2) of the yellow solid that appeared at xcex4 194.1, 154.1, 153.2, 147.6, 143.3, 126.4, 114.5, 110.5, 96.5, 56.4, 56.2, 56.0 clearly indicated the presence of 12 carbons as similar to the 12 carbons of xcex2-asarone except that the position of side propyl group which appeared at xcex4 194.1 (C-3xe2x80x2), 154.1 (C-1xe2x80x2) and 126.4 (C-2xe2x80x2) could be possible due to xcex2-unsaturated aldehyde (xe2x80x94CHxe2x95x90CHxe2x80x94CHO) group. The EI mass spectrum (FIG. 3) of yellow solid showed a clear [M]+ peak at m/z 222. On the basis of above spectral data, the yellow solid was postulated to be 2,4,5-trimethoxycinnamaldehyde as a trans-isomer (Example I). The formation of this unexpected trans-2,4,5-trimethoxycinnamaldehyde was finally confirmed by its (i) oxidation with neutral KMnO4 in the cold acetone to well known 2,4,5-trimethoxybenzaldehyde (Example II) (Birch, A. J., Jackson, A. H., Shannon, P. V. R. and Steward, G. W., Journal of Chemical Society Perkin Trans I, 2492-2501, (1973) and Starkovsky, N. A., Journal of Organic Chemistry, 27, 3733-3734, (1962)) (ii) direct oxidation of xcex2-asarone with selenium dioxide (Liu M C, Lin T S and Sartorelli A C, J Med Chem, 35, 3672 (1992)) into 2,4,5-trimethoxycinnamaldehyde (Example III) and its comparison with reported natural cinnamaldehyde. Treatment of xcex2-asarone with selenium dioxide and few drop of base such as pyridine, triethylamine etc in dioxane gave two distinguished spots on TLC plate in which one yellow spot is expected for 2,4,5-trimethoxycinnamaldehyde while minor spot for corresponding cinnamyl alcohol derivative as clearly confirmed by the absorbance of peak at 1648 (carbonyl) and 3480 (hydroxyl group) in IR spectra. The latter was formed even when the amount of selenium dioxide was increased up to 1.3 equiv. Formation of side product alcohol are common with aldehyde during the allylic oxidation of several analogs of xcex2-asarone with SeO2. However, we observed that without any separation, treatment of the mixture of cinnamaldehyde and cinnamyl alcohol with pyridinium chlorochromate (PCC) (Lin, S. J., Short, R. E., Ford, S. P., Grings, E. E. and Rasazza, P. N., J Nat Prod, 61, 51-56 (1998)) afforded 2,4,5-trimethoxycinnamaldehyde as a single spot since alcohol got oxidized into cinnamaldehyde. The 1H-NMR spectral data of cinnamaldehyde is similar to the reported natural (Kulkarni, M. M., Sohani, J., Rojatkar, S. R. and Nagasampagi, B. A., Indian J. Chem., 25B: 981-982 (1986)) and its 13C-NMR spectral data is reported here for the first time. Thus, isolation and characterization of above cinnamaldehyde has opened a new route to prepare several substituted cinnamaldehydes in a single step starting from phenylpropane derivatives.
After successful assignment of substituted cinnamaldehyde, the applicants main attention was focused on to increase the percentage of cinnamaldehyde (a natural dye) as demand of natural colourants over synthetic ones are increasing worldwide due to their safer and ecofriendly nature. Thus, we observed that treatment of phenylpropane with DDQ ranging from 1 to 20 moles (preferably 1.5 to 8 moles) afford mainly cinnamaldehyde. The formation of unsaturated aldehyde from saturated propane side chain is possible only via initial formation of phenylpropene which further undergo oxidation and lead to the formation of cinnamaldehyde in a single step. The yield of cinnamaldehyde may be further increased by using the catalysts such as mineral acid (hydrochloric acid, sulfuric acid) or Cu(I) or Fe(III) salt or periodic acid or organic acids such as acetic acid, propionic acid, butyric acid, ion exchange resin such as IR-120H, a sulphonated polystyrene resin, para-toluenesulphonic acid (PTSA) etc. The formation of cinnamaldehyde can be carried out in a short time by adsorbing the solution of 1-Propyl-2,4,5-trimethoxybenzene and oxidising reagent DDQ on the following solid support namely celite, silica gel, molecular sieve, alumina under microwave irradiation (Posner, G. H. and Rogers, D. Z. J. Am. Chem. Soc. 99, 8208 (1997); Jr. Filippo, J. S. and Chern, C. I. J. Org. Chem. 42, 2182 (1979) (Example IV) for 40 second to 20 minutes, preferably 2 to 12 minutes. It is worthwhile to mention that among several oxidizing reagents (such as manganese dioxide or p-chloranil or Pyridinium chlorochromate or tBuOOH CrO3), DDQ is found as a powerful dehydrogenating (Sondengam, B. L. and Kimbu, S. F., Tetrahedron Letters, 1: 69-70, (1977) and Guy, A.; Lemaire, M. and Guette, J. P., Chem. Commun. 8 (1980)) and oxidizing reagent (Becker, H. D. J. Org Chem. 30, 982 (1965)) which converts phenylproane derivatives into corresponding cinnamaldehydes as a trans-isomer (Lemaira, M., Guy, A. and Imbert, D., Chem. Commun. 741 (1986) and Ireland, R. E. and Brown, G., Org. synthesis, Coll. Vol. V, 428-431)) in one step. In addition, the DDQ-mediated reactions allow to monitor the progress of the reaction as a green-coloured charge transfer (CT)-complex formed, which gradually changes to pink or brown color (as the 2,3-dichloro-5,6-dicyano-1,4-hydrobenzoquinone crystallized out), indicates the formation of desired products. At the end of the reaction, the precipitated hydrobenzoquinone (DDQH2) can be easily separated by filteration which allow to obtain 2,3-dichloro-5,6-dicyano-1,4-hydrobenzoquinone (DDQH2) in 90 to 94% yield. The amount of precipitated hydroquinone (DDQH2) can be conveniently converted back to DDQ in good yield by standard methods (Walker, D. and Waugh, T. D., J. Org. Chem. 30, 3240, (1965)). In view of all above, the DDQ-mediated conversion of phenylpropane into cinnamaldehyde appears to be industrially attractive method. In addition, hydrogenated crude calamus oil (asarones present from 70 to 96%) can be used directly for oxidation by DDQ for the preparation of 2,4,5-trimethoxycinnamaldehyde is an added benefits since remaining constituents of reduced calamus oil do not interfere during oxidation and the yield was found to be less than just by 5-15% depending upon asarones percentage in calamus oil. Therefore, this invention makes above process further cost effective. 
Thus, applicants the present method for the synthesis of substituted cinnamaldehyde is not only simple, cheaper and high yielding but can convert any, kind of substituted phenylpropanes which are even prone to acid or base.